To reload your icons, simply bring up your model selection within the game like if you were about to spawn a model.Keep holding down Q and press a model's icon in the list WITH THE RIGHT MOUSE BUTTON.Doing so will bring you a drop-down menu where you will be able to reload the spawn icon.Hover over the option and select your choice:

If you wish to simply reload the icon you've selected, press "This Icon".If you wish to reload all of the icons displayed, press "All Icons".

Beware that reloading all icons may take up a considerable ammount of time.Icons are also rendered with the cubemap you are currently displaying (e.g. If you render in the gm_construct area, the sunshades on TnB models will show a reflection of that area), for optimal resolution I would suggest a sunny map with integrated cubemaps.